Induction crucible furnace comprising a rammed crucible



United States Patent O U.S. Cl. 13--27 4 Claims ABSTRACT OF THE DISCLOSURE A crucible structure made from rammed material for use as an induction furnace is surrounded by an induction coil, and a ceramic cylinder provided with longitudinally extending passageways is interposed between the wall of the crucible and the induction coil. A layer of watertight and mechanically strong material such as micanite is interposed between the ceramic cylinder and the coil, and a layer of thermally insulating and water-permeable material such as asbestos is interposed between the ceramic cylinder and the crucible. The passageways in the ceramic cylinder open inwardly to the water-permeable layer and serve to drain off any water which occurs during sintering and the watertight layer prevents any of the water from reaching the induction coil.

Two different fundamental forms of construction of induction crucible furnaces comprising a crucible of rammed ceramic composition exist. In one form, the induction coil surrounding the crucible is inwardly screened, by a cylinder of mechanically robust and watertight material, from the water issuing from the rammed composition of the crucible, the draining of this water being greatly impeded and slowed down thereby, thus red-ucing the durability of the crucible. In the other known form of furnace construction, drainage of the water between the turns of the coil is facilitated deliberately. This offers the advantage that the prepared crucible can dry rapidly, which affects its durability favorably, but has the disadvantage on the other hand that the coil insulation becomes damp temporarily and must accordingly be stronger.

The purpose of the present invention is to eliminate the aforesaid disadvantages of the forms of furnace construction known until now.

According to the invention, we provide an induction crucible furnace comprising a rammed crucible, which is surrounded by an induction coil, in which a cylinder of ceramic material endowed with longitudinal holes or passages which are open on the inward side of the said cylinder along at least a part of their length is situated between the said rammed composition and the said induction coil, an intermediate layer of mechanically robust and watertight material being situated between the said cylinder and the said induction coil, and an intermediate layer of solid, thermally insulating and 3,457,356 Patented July 22, 1969 lCC water-permeable material being situated between the said cylinder and the said rammed composition.

The invention will now be described in detail with reference to the accompanying drawings, which illustrate the invention, but in no restrictive sense. In the drawings:

FIGURE l shows an induction crucible furnace according to the invention in longitudinal section.

FIGURE 2 shows the same in cross-section, and

FIGURES 3 and 4 illustrate elevational views of two different forms of ceramic segment plates.

The numeral 1 marks the furnace crucible `formed of a rammed composition, which is surrounded by an induction coil 2. Within the induction coil 2 is situated a cylinder 3 which is preferably assembled from segmentshaped ceramic plates 4. As is apparent from FIGURE 2, the cylinder 3 comprises a number of uniformly distributed longitudinal holes or passages 5, which are in communication with the inward surface of the cylinder at least along a part of their length. Between the ceramic cylinder 3 and the induction coil 2 is situated a watertight and mechanically robust intermediate layer 6, for example consisting of socalled micanite or of an analogous substance. On the inward side of the cylinder 3 is situated another intermediate layer 7, of thermally insulating and water-permeable material, e.g. asbestos, whose primary function is to screen off the longitudinal holes or passages 5, so that these cannot be lled or clogged with rammed crucible composition, which might prevent draining of the water from the composition.

FIGURE 3 shows one form of ceramic plate 4 in which the longitudinal passages 5 are open throughout their length towards the rammed composition of the furnace crucible, whereas in the form of plate according to FIGURE 4, the longitudinal passages 5 are open to the inward surface of the cylinder 3 and towards the rammed composition of the furnace crucible 1, through slots 9 distributed uniformly along their length.

A displacement in outward direction of the water present in the rammed crucible composition occurs during the sintering of the crucible. The water passes through the intermediate layer 7 and finally encounters an unobstructed draining path leading downwards in the vertical longitudinal passages 5 in the ceramic plates 4, without coming into contact with the induction coil 2. A furnace may thus be operated at full voltage from the start, with a new crucible. The durability of the crucible specified is considerably greater than in the case of conventional crucible furnaces.

We claim:

1. An induction crucible furnace comprising a rammed crucible, which is surrounded by an induction coil, in which a cylinder of ceramic material endowed with longitudinal holes or passages which are open on the inward side of the said cylinder along at least a part of their length is situated between the said rammed composition and the said induction coil, an intermediate layer of mechanically robust and watertight material being situated between the said cylinder and the said induction coil, and an intermediate layer of solid, thermally insulating and water-permeable material being situated between the said cylinder and the said rammed composition.

2. An induction crucible furnace as claimed in claim 1, in which the said cylinder is assembled from segmentshaped ceramic plates.

3. An induction Crucible furnace as claimed in claim 1 or 2 in which the said longitudinal passages within the said cylinder are open through slots along their entire length on the inward surface of the said cylinder.

4. An induction crucible furnace as claimed in claim 1 or 2 in which the said longitudinal passages in the said cylinder are open on the inward surface of the said cyllinder through individual slots which are uniformly distributed along their' length.

References Cited UNITED STATES PATENTS 3/1931 Davis 13-27 6/1934 Willcox 13-27 ANTHONY BARTIS, Primary Examiner L. H. BENDER, Assistant Examiner U.S. C1.X.R. 13-26 

